1. Field of the Invention
This invention relates to an apparatus for the inhalation of powders to be used for the direct administration of drugs to the respiratory tract.
2. Description of the Related Art
The administration of drugs by inhalation plays an important role in the treatment of respiratory disorders.
The action of the drug is in fact more rapid and, moreover, prolonged by this route. Local administration to the target organ also means that it is possible to use much smaller quantities of the active principle, with less frequent side effects.
The delivery systems available for local administration of drugs to airways are nebulizers, metered dose inhalers and powder inhalers.
Nebulizers provide effective treatment, but as a result of their dimensions they are restricted to domestic use.
Metered dose inhalers are of small dimensions and are easily portable, but the correct use thereof requires perfect coordination of inhalation and of aerosol release, and thus many patients have difficulties in employing them properly.
The dry powder inhalers constitute a valid alternative for the administration of drugs to the airways.
The essential advantage of powder inhalers is that they do not require coordination of movements, as release of the active principle is operated by the patient's inhalation.
One common feature of powder inhalers is that they are activated by a turbulent air flow generated by inhalation by the patient.
This air flow created in the interior of the inhaler carries out the drug, contained in appropriate dosage units or chambers in the form of micronized powder.
Devices for the inhalation of powders can be divided into two basic types according to the dispensing and delivery means for the active principle:
I. Single dose inhalers for the administration of subdivided doses of the active compound enclosed in hard gelatine capsules.
II. Multidose inhalers preloaded with quantities of active principle sufficient for complete treatment cycles, each single dose being distributed in a practical and rapid manner at the time of use, according to the dosage program, allowing, where required, for the administration of two doses simultaneously.
The delivery apparatus is disposable at the end of the treatment cycle.
As a result of their relatively complicated structural mechanisms, the inhalers of type I (examples of which are described in EP 41783 (Fisons), BE 813143 (ISF), GB 2064334 and BE 886531 (Glaxo), EP 147755 (Boehringer) and EP 271029 (Mect) are relatively difficult for patients with poor manual dexterity.
Moreover, in view of the fact that the dose of the drug to be inhaled is enclosed in a capsule of gelatine, they present some significant disadvantages:
the inhalers have to be charged with the unit dose before each use and each time the operation is completed they must be empty and clean from any capsule and powder residue; PA1 the capsule is often not split correctly on the first attempt and the patient has to perform several operations; PA1 the capsule is often not emptied completely, and the dose delivered is not constant. PA1 a nozzle which is free to rotate on a main body; PA1 a storage chamber for the medicinal substance, of such a volume that it contains a sufficient quantity of the drug for a complete treatment cycle; PA1 a dosing means which, during each rotation through 180.degree., delivers one dose of the medicinal substance; PA1 a dispensing system which, during the rotation, pours the dose into a collecting chamber in communication towards its top with the cavity of the nozzle and towards its bottom with a ventilation chamber, itself in communication with the outside by means of two symmetrical holes.
An apparatus of type II, which, has proven to be advantageous for the administration of powdered medicinal substances, is described in the Applicant's British Patent No. 2041763.
The apparatus consists essentially of the following elements:
In operation, the patient rotates the nozzle on the central body through 180.degree., thereby effecting distribution of the dose, then inhales via the nozzle, generating an air flow which takes up the powder and carries it out along the central cavity, from where it is inhaled directly upon the act of inhalation.
European Patent Application No. 87850060 (Aktiebolaget Draco), filed after Applicants' above-identified British patent, describes an inhaler, whose working depends substantially upon the presence of deflector devices comprising helical elements intended to ensure effective disintegration of the powder aggregates into particles suitable for inhalation and for reaching the deeper parts of the respiratory tract.
This apparatus does not in fact have any particular advantages compared to the device known beforehand.
The deflector devices do not constitute a real improvement, since the inhaler of British Patent No. 2041763 already provides for the presence in the interior of the central conduit of helically extending blades to impart a turbulent motion to the powder composition.
Moreover, the Draco inhaler is characterized by a certain structural complexity and is particularly designed for the administration of small doses of powder, less than 1 mg upon each actuation.
An inhaler of the multidose type in which the individual doses of powder are contained in each of a series of plastic blisters is described in Glaxo's EP 211595.
This case also relates to a rather complex apparatus, the operation of which may present problems for the patient and may be accompanied, as in the case of the inhalers of type I, by disadvantages, such as incorrect opening of the container holding the drug, with a consequent lack of uniformity of the dosage and loss of the active powder in the interior of the internal cavity.
The ideal inhaler, on the other hand, should allow for constant and correct administration of the drug, with minimum effort on the part of the patient.
A multidose device for the inhalation of powders of type II, if actually operational and well designed, has real advantages and is extremely suitable by virtue of its simplicity of operation (requiring no particular skill on the part of the patient), the constancy and reproducibility of the dose delivered by means of an efficient distribution system, and the absence of waste arising from the opening of a capsule or blister.